It was a China wracked by war, famine and exile, but the Emperor of Manchukuo rarely got up before midday, ate his dinner at midnight and was addicted to drugs.

'People thought that, with my nocturnal lifestyle, I was smoking opium. This was a misunderstanding. No, I was addicted to drugs, both Western and Chinese - external, internal and injections, I took them all. I loved the drugs of Bayer.'

So reads the celebrated 'autobiography' of Pu Yi, the head of the Japanese puppet state of Manchukuo between 1932 and 1945 and China's last emperor. From Emperor to Citizen was always said to have been written from his prison cell in the 1950s. Last month, the Masses Publishing House re-issued its 'grey copy' - a version it first produced in January 1960 for limited circulation among political and legal cadres and historians.

The standard version was published in Putonghua in March 1964 and went on to be translated into many languages, selling nearly two million copies. It is a startling account of how the emperor of the world's largest nation turned into a man in a blue padded jacket weeding vegetables in a Beijing garden.

But now it has come to light that this version was not written by Pu Yi but by an editor at MPH, part of the Ministry of Public Security. It was then subjected to a rigorous revision and censorship process by dozens of scholars and officials. They removed 100,000 words from the original version to meet the political needs of the time and the demands of Pu Yi himself, mainly material relating to his personal life, Japanese spy organisations in China and his testimony at the International Military Tribunal for the Far East from 1946-1948.

The 'grey copy' is said to be the closest to Pu Yi's original text.

The motives of MPH in revealing this now are both commercial and historical. The 'grey copy' is an important piece of China's history. Liu Can, vice-chairman of MPH, said that they wanted to ensure history was shown in its true light.

'We know the old people involved in this story are disappearing one by one. Publishing this book is like saving history.'

In addition, the political objective of the 1964 version - to show how Communism can transform an individual - has long disappeared. In the China of 2011, it appears quaint and almost ridiculous.

Pu Yi wrote the original during his nine years in prisons in Fushun and Harbin after being repatriated from the Soviet Union in 1950. The Soviet army captured him on August 16, 1945, at Shenyang airport, when he was about to board a plane to take him to Japan, one day after the surrender of Emperor Hirohito.

In the original, 449 pages long, he describes life from his birth in the palace, to his brief three-year tenure as emperor, his expulsion from the Forbidden City in 1924 and his installation as the emperor of the puppet state of Manchukuo in March 1932 until his arrest.

He wrote out of deep remorse over his past life and under pressure from his captors. He was helped by his brother Pu Jie and other former high officials of the Manchukuo government imprisoned with him.

The prison officers gave the text to a division of MPS which considered it a detailed history of the former emperor; they passed it to the MPH. The text came to the attention of the leaders in Zhongnanhai, who realised what a jewel they had unearthed.

The new state was just 10 years old and, in the midst of the Cold War, cut off from the Western world, which was hostile and had given China's place at the United Nations to Taiwan. The leaders realised how Pu Yi could be a dramatic example of how Communism could transform a person, even a former emperor, and explain their revolution to a suspicious and unbelieving world.

The leaders ordered the amnesty of Pu Yi on December 4, 1959, and gave him a two-week tour of the country before his return to Beijing. The chief editor of MPH invited him to his office, explained the project and introduced him to Li Wenda, the editor who would write the book.

In April 1960, Li rented a room in the Xiangshan Hotel in western Beijing. Each afternoon Pu Yi took time off from the nearby vegetable garden where he was working, to answer Li's questions. 'I found his expressions of remorse too excessive and could not follow how this came about and why his opinions changed,' Li later wrote in his own memoirs. Li and an assistant went to northeast China for nearly two months to conduct interviews and research the book. It was Li who conceived the idea that the book should show the success of the party in transforming a war criminal; also he did not want foreign readers to know the great pressure Pu Yi had been put under in prison.

Li threw himself heart and soul into the work, which it took him three years to complete. The publishing house sent the manuscript to the censors and invited more than 20 experts and scholars to review it. It was decided to remove more than 100,000 words, in the interests of political correctness and at the request of Pu Yi. On April 30, 1962, he had married Li Shuxian, a hospital nurse, and did not want her to know all the details of his private life.

Among the episodes removed was the fact that his first wife, Wan Rong, had become pregnant by another man. He had the baby removed at birth and thrown into a boiler. He told Wan that his brother had adopted the child and insisted she make monthly payments for his upkeep.

In the original version, he wrote that he had only discovered his wife's pregnancy in 1935 when she was close to giving birth. 'My feelings at that time were hard to describe,' he says. 'I was angry but did not want the Japanese to know. All I could do was express this anger against her in person.

'Until her death, she kept having the same dream, in which her child was living next to her. After the end of the war and our separation, her opium addiction worsened and her body became weaker. She died of illness in 1946.'

In February 1964, Li received 5,000 yuan for his four years of intense work and, in March, the book was finally published, with Pu Yi's name on the front. It was a very different product from the one he had written in prison.

It become a global publishing sensation. The world was fascinated by the story of how the Son of Heaven and ruler of a quarter of the world had lost his throne, become a war criminal and was transformed into an ordinary citizen.

Unlike the Soviet Union's assassination of Tsar Nicholas and his family, China had spared its emperor and given him the chance to live a normal life and tell his story.

It inspired the film The Last Emperor in 1987 by Bernardo Bertolucci, at a cost of US$25 million (HK$ 194million). The director was fortunate to obtain the approval and co-operation of the government, which allowed him to work in the Forbidden City. While he was filming the immense coronation ceremony, Queen Elizabeth was visiting Beijing; as a result, she was unable to see China's most famous monument.

The film involved 19,000 extras, including soldiers of the People's Liberation Army. The story and the experience of filming it proved a moving experience for many of those involved. 'It was a difficult film to emulate and I have never been to that pinnacle of a certain type of film,' recalled Jeremy Thomas, the producer. 'I doubt if I ever would or could make a film like that again.'

After the publication of the book, Pu Yi was allowed to receive foreign guests and worked in the literary department of the Chinese People's Political Consultative Conference.

During the Cultural Revolution, he was a natural target for the Red Guards as a symbol of imperial China. While the local police protected him from physical attack, his quality of life and emotional state deteriorated.

He died on October 17, 1967, in Beijing of complications arising from cancer of the kidneys and heart disease. He was 61 years old.